Phenothiazine is typically manufactured in flake form. Such flakes are formed by coating molten phenothiazine onto a drum flaker, where the product is cooled, and crystallizing the product to a solid which is flaked. The product is then conveyed to a physical separation process in which the product fines (powder) are separated from the flakes typically by the use of sizing screens. The product is then packaged and shipped to customers who convey or transfer the flakes through their own processing equipment. Despite product classification, the flakes tend to contain up to about 6% of product fines after manufacture. Further, the flakes are prone to further breakdown into fines during subsequent shipping and handling.
The generation of product fines or powder in the flake phenothiazine product presents problems. Flake products containing such fines suffer from the deficiencies of non-uniform particle size, caking, dustiness and clumping. Phenothiazine is a respiratory, skin, eye and gastrointestinal irritant and skin sensitizer, and is more likely to cause such problems when in the form of fines. Product fines in the flake product also increase the likelihood of product explosiveness. Flake product containing high levels of powder (i.e., greater than about 6% particles having a particle size of less than about 500 microns) is also prone to caking or clumping.
Non-uniform particle size in flaked product increases the tendency of the product to cake and/or clump and to resist ready flow transfer both internally and at customer facilities. The caking and/or clumping of the product makes it difficult to discharge from containers such as bins, bags, trucks, storage silos and the like and difficult to transfer. It may also have a tendency to bridge or block in containers. Product fines also present safety, health and environmental issues. From a safety standpoint, product fines are of particular concern due to the increased risk of explosion, as well as increased risk to employee health with respect to increased risk of skin irritation and skin sensitization and the like as noted above.
In accordance with the foregoing, there is a need in the art for a method to produce phenothiazine which reduces the problems associated with powder and fines in the finished product, but which still produces high quality phenothiazine. There is also a need in the art to reduce the problems associated with caking and/or clumping of phenothiazine product during shipment, transfer and storage.